This invention relates to a dowel formed in the shape of a tube for insertion into annular recesses formed in pieces of material to be joined together by the dowel. The tubular dowel may also be combined with other attachment elements such as screws, bolts, nuts, brackets, etc., to also join two pieces of material together in an abutting relationship.
Cylindrical-shaped dowels have long been used to form so-called dowel joints in which two pieces of material are joined together in an abutting relationship. The dowel joint consists of aligned bores formed in the two pieces of material for receiving respective ends of the dowel, together with an adhesive, so that the two pieces may be firmly held together.
The above-described cylindrical dowel system has proven fairly effective in constructing furniture and other articles not likely to be subjected to rough use or excessive stress. Such dowel system has also been used in constructing and holding together stairwell systems which, as expected, are subjected to greater stresses. In these latter uses, the dowel system may be more likely to separate either by reason of the breaking or fracture of the dowel, breaking or fracture of one or both pieces of material joined together because of the weakening of the material as a result of forming the bores therein, or the pulling of the dowels from the bores. This latest event could occur, for example, because of insufficient surface areas between the dowel and the bore walls covered by adhesive.
A number of proposals have been made to increase such surface areas or otherwise improve the holding ability of the dowel joint. In E. D. Tyler, U.S. Pat. No. 77,337, a tubular metal "dowel pin" is disclosed for insertion in rings or annular recesses formed in two pieces of material to be joined together, the object being to increase the strength of the joint by preservation of material which would otherwise be drilled out to form bores rather than annular recesses. However, in order to join the two pieces of material together in proper alignment, the annular recesses must be precisely aligned, and this is difficult to achieve. In U.S. Pat. No. 3,756,635, issued to Howard L. Beers, a three piece dowel apparatus is disclosed for better distributing adhesive over the surfaces of the apparatus to join two pieces of material together. Of course, three pieces of material are now required where before a single dowel was utilized and thus obviously would increase the expense of the dowel joint.